<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script type="text/javascript" src="./vue.js/vue.js"></script>
    
</head>
<!-- 准备好一个容器-->
<div id="root">
    <h2>今天天气很{{ info }}</h2>
    <button @click="changeWeather">切换天气</button>
</div>


<script>
	const vm = new Vue({
        el:'#root',
        data:{
            isHot:true,
            info:'炎热'
        },
 /*        computed:{
            info(){
                return this.isHot ? '炎热' : '凉爽'
            }
        }, */
        methods: {
            changeWeather(){
                this.isHot = !this.isHot
            }
        },
        watch:{
            isHot:{
                immediate: true, // 初始化时让handler调用一下
                // handler什么时候调用？当isHot发生改变时。
                handler(newValue, oldValue){
                    console.log('isHot被修改了',newValue,oldValue);
                    this.info=this.isHot ? '炎热' : '凉爽'
                }
            }
        } 
    })
</script>

</html>